Single camera activity maps have long been used to show the density of objects of interest (e.g., people, vehicles, etc.) moving in an area. As displayed in heat map form, these maps indicate relative activity over time with respect to spatial locations. For building safety, activity maps are used to learn of bottlenecks in building escape routes that delay mass exit. For retail, activity maps are used to examine common paths of shoppers (such as, e.g., which shop windows shoppers pause at, what displays can entice a detour, etc.). For public spaces, activity maps are used to distinguish between areas of congregation and paths of movement.
In addition to density, activity maps provide other activity features that may be useful. For instance, pseudo-color maps have been used to distinguish path directions in active areas. However, density remains the most popular feature.